Core elements for automotive body parts have generally been manufactured of metal tubing or solid foam thermoplastic cores. With the desire to reduce the weight of automobiles, It is preferable to produce and process and core elements which are light weight.
One prior art process includes inflatable bladder about which organic polymeric materials may be molded. The bladder is either deflated and pulled out or left for waste after molding. The bladder is generally resilient and flexible, such as a balloon. Therefore, a specific shape can not be maintained by the bladder during the molding step.
Blow molding articles is also commonly known. In general, a parison is formed by the injection of a plasticized material around a mandrel. While the material is still molten and on the mandrel, it is transferred to a blowing mold where air is used to inflate it forming the article.